S&W Mod 4563 and Mod 1006 Question

I notice on both pistols that when you are shooting in single action, with the hammer cocked manually and starting to squeeze the trigger, about one third to halfway through the trigger pull there is a very noticeable "click" as if something is setting inside to fire. When you continue the trigger pull, the pistol will of course fire.

I own several firearms, including many S&W Pistols and don't have that feeling or click on others.

Is this perhaps something on newer pistol designs and if so, what is the purpose? :D